WASHINGTON: Uited States (US) Senate Democrats have written a letter to US President Donald Trump saying that any agreement with North Korea must include the dismantlement and removal of its nuclear weapon.

The letter said, "Any agreement with North Korea must build on the current test suspension and ultimately include the dismantlement and removal of all nuclear, chemical, and biological weapons from North Korea," as per Sputnik.

US senators also warned of tougher sanctions on North Korea if US President Donald Trump's deal wouldn't mandate complete denuclearisation.

US Defence Secretary Jim Mattis said the sanctions imposed on N Korea could only be lifted after Pyongyang realises that it has taken irreversible steps to denuclearisation.

Last week, Trump reinstated the planned summit with North Korean leader Kim Jong-un saying, the relationship between the US and N Korea will start on June 12.

The two leaders are expected to discuss denuclearisation of North Korea in the June 12 summit.